The present invention relates to intraocular lenses, particularly to methods for attaching a haptic to an optic using laser welding.
Intraocular lenses have been known since about 1950. They are used to replace the natural lenses of eyes which have been damaged by trauma or disease, such as cataracts. A typical intraocular lens (IOL) comprises an artificial lens ("optic") and at least one support member ("haptic") for positioning the IOL in the eye. The optic may be formed from any of a number of different materials, including polymethylmethacrylate (PMMA), and it may be hard, relatively flexible or even fully deformable in order to permit the IOL to be rolled or folded and inserted through a relatively small incision in the eye. The haptic is generally made of some resilient material, such as polypropylene or PMMA. IOL's may be characterized as either "one-piece" or "multi-piece." In the one-piece IOL's, the haptic and the optic are integrally formed and the IOL is then cut to the desired shape and configuration. The multi-piece IOL's are formed either by attaching the haptic to a pre-formed optic or by molding the optic around an end portion of the haptic.
U.S. Pat. Nos. 4,834,751 and 4,894,062 (both Knight, et al.) describe haptic attachment methods whereby a haptic and an anchoring member are joined, then an optic is molded around the end portion of the haptic having the anchoring member joined. While these methods provide strong haptic-optic interlock, the procedure for molding an optic around previously joined haptic and anchor members is complex and requires special care to maintain the haptic in place while the optic material is being cured and to remove the mold without damaging the haptic.
Many methods for attaching a haptic to a pre-formed optic are known, including those involving the use of adhesives. If an adhesive is used to attach a haptic to an optic, the adhesive must be strong, biologically inert and resistant to degradation by bodily fluids. At present, there are few materials which would satisfy all these requirements. In addition, there is a danger that the adhesive would deteriorate over time, resulting in loose or detached haptics within the eye.
Other, more common, methods for attaching a haptic to a pre-formed optic involve the use of heat. One such haptic attachment method involves drilling intersecting holes into the periphery of an optic and inserting one end of the haptic into one of the holes. A heated probe is then inserted through the other hole, contacting the haptic and causing a portion of it to melt into the second hole. When the haptic end portion hardens, a mechanical interlock with the optic is formed. A similar method is disclosed in U.S. Pat. No. 4,104,339 (Fetz, et al.), where a haptic hole is made in the peripheral edge of an optic, the haptic end is inserted into the hole and then an inductively heated thin probe is pushed through the posterior face of the optic into contact with the haptic end to form a fused connection between the haptic and the optic. This is currently the most common method for attaching a haptic to an optic.
Another such method is disclosed in U.S. Pat. No. 4,307,043 (Chase, et al.), where a hole having threaded recesses is made through a portion of the optic (the hole being essentially parallel to the plane of the optic) and one end of a haptic is inserted through the hole so that it projects beyond the optic. Heat is then applied to the haptic end projecting beyond the optic to melt a portion of it, which fills the threaded portions of the hole. When the haptic material hardens, a mechanical interlock with the optic is formed.
These heat attachment techniques described above are disadvantageous in that skilled technicians are required and/or there is danger of damage to the optic.
U.S. Pat. No. 4,786,445 (Portnoy, et al.) discloses another haptic attachment method which involves making a cavity in the periphery of an optic, wherein the innermost portion of the cavity has a shoulder. A haptic end portion is inserted into the cavity and laser energy of a near infrared wavelength is transmitted through the optic to the haptic, causing it to melt and flow into the shoulder of the cavity. When the end portion hardens, a mechanical interlock between the haptic and the optic is formed. Although this method avoids some of the problems of the prior-mentioned methods, there are other disadvantages. Because the haptic end is melted to form a shoulder within the cavity of the optic, there is a likelihood of variation in haptic length, both between individual IOL's and between individual haptics attached to the same IOL.